Problem: Reduce to simplest form. $-\dfrac{7}{8}-\left(-\dfrac{5}{6}\right)=$
Solution: $=-{\dfrac{7\cdot3}{8\cdot3}} +{\dfrac{5 \cdot 4 }{6 \cdot 4}}$ $=-{\dfrac{21}{24}}+{\dfrac{20}{24}}$ $=-\dfrac{1}{24}$